1. Field of the Invention
The present invention concerns a method of measuring the surface or interface tension between two fluids and a device for implementing the method.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
The tension measured is referred to as “surface tension” for a gas-liquid system and is referred to as “interface tension” for a liquid-liquid system.
The invention can be applied in numerous economic fields, for example for producing cosmetics, detergents, pharmaceutical or chemical products, measuring apparatus in public or private research laboratories, in higher education for practical work and in general terms in all sectors that require to define the fundamental properties of a liquid-liquid or liquid-gas interface, such as rigidity, visco-elasticity, deformability, etc.
Numerous techniques for measuring the interface tension between fluids are already known, such as for example:                measurements by visualisation (for example the hanging drop technique)        tensile force measurements by Wilhelmy plate or by Du Noüy ring on a plate        measurements based on Rayleigh instability such as the oscillating jet technique, or on the change in polarisation of the electromagnetic waves at the interface, this is the ellipsometry technique.        
Some techniques are based on the Laplace equation for calculating the droplet volume and the maximum bubble pressure. These techniques use digitisation and computer processing such as the drop profile, the bubble profile and even the microfluid tool.
Unfortunately these techniques, through their use of a large sample of fluid and through the size of the devices, prevent measurement at high temperatures. Moreover, the liquid medium must often be transparent. In particular these techniques do not apply or are too imprecise in the case of viscous and/or elastic liquids.
To remedy these drawbacks, the invention proposes a novel microscopic technique of measuring surface or interface tension making it possible to measure this quantity with precision at high temperatures (above 50° C.) and aims it the following objectives:                rapidly measuring the interface and surface tension,        requiring very little fluid for making the measurement,        allowing heating of the microsystem for achieving high temperatures,        applying to an opaque and/or viscous liquid.        
The objectives in use referred to above are highly advantageous for applications where liquids have high added values or have solid phases at ambient temperature (cosmetics, pharmaceutics, petrochemicals, etc.).